The present invention refers to a process for manufacturing pre-cured parts of composite material with green-applied stiffeners, in which at least two parts manufactured in composite materials are structurally bonded, of which a first part called base part or support is cured and a second part called stiffener is in green condition and in which the bonding of both parts is carried out by means of a structural adhesive sheet in such a way that the second part is compacted against the first part, with adequate crosslinking of the resin of its composite material and so strongly adhered to the skin of the first part that the adequate resistance of the adhesive sheet is assured.
More specifically, the object of the invention is to develop the necessary theoretical concepts and their corresponding manufacturing processes to obtain a bonding system by co-gluing two or more structural parts manufactured from composite materials.
The bond is carried out by means of autoclave curing of a structural adhesive sheet interposed between two surfaces of parts made of composite material. The resin is cured in one of these parts and green in the other one. The curing of the resin of the part which is in a green condition is also produced in the same autoclave cycle.
One of the most productive industrial applications of the present invention is the manufacture of large size structural members where the quality of the base part is assured, that is, the part arriving already cured to the process.
The adhesive joints of structural components have a reduced application in composite materials due to the fact that their use and development degree is limited as corresponds to their recent appearance in the technical background.
In the case of co-gluing, the applicant""s closest background refers to the bonding of spar stiffeners of the horizontal stabilizer torsion box for the Airbus A330-340 aircraft (currently in production), the bonding of the longitudinal stiffeners of the skin of the wing torsion box for the CASA 3000 aircraft (in prototype stage), the bonding of spars to the wing skin of the EFA-European Fighter Aircraft (in pre-production phase) and the bonding of the FB.5-1 test box of the LFS-Large Flying-Surfaces development program.
From the results of the previous experiments as well as from other studies and manufacturability tests, it is deduced that the application of the process of the present invention is both achievable and reliable for its use in parts with highly demanded resistant structures and with strict quality requirements.
This invention is applicable to the manufacture of structural members of composite material parts in which one or several of its components are in a cured condition (base components) and the other components are in a green condition (stiffener components), provided that the bonding between both of them is made. These parts may be any of those belonging to:
Aircraft structures and controls such as flying-surface contours, spars, ribs, fixtures.
Space vehicles.
Marine and land vehicles.
Industrial machinery and equipment.
The manufacturing processes involved are:
Laminating of composite material (manual or automatic).
Cutting of composite material.
Hot forming of composite material.
Handling and positioning of parts and tooling.
Autoclave curing.
The used materials may be integrated by different resins and different types of fibre, such as:
Fiberglass.
Carbon fibre
Kevlar fibre
Boron fibre
Epoxy resin.
Thermoplastic resin
Other heat-stable resins
The object of the invention is a manufacturing process for composite material parts in which at least one green part is adhered (stiffener component) with another cured part (base component) by means of a structural adhesive. This bonding is obtained by the moulding and pressure application with special tools designed for such purpose, so that it is possible to control and retain the resin and adhesive flow produced during the autoclave cycle.
The green part will have an L- or T-shaped cross section. The process for the latter will be described in detail below.
The cured part may be a wing skin or that of a stabiliser or any other component needing to be stiffened in order to comply with its structural function.
The co-stiffener with a T-shape is confined by devices (angle pieces) which are the basis of the system and which control and retain the resin flow. Afterwards, a vacuum bag is fitted as will be explained later on, and the assembly is introduced into an autoclave to submit it to a curing cycle under a predetermined pressure and temperature depending on the material and part requirements.
The process is applicable to the parts obtained by any lamination process (manual or automatic).